Thermophysical Studies Research Articles

Modeling thermal conductivity of nanofluids using advanced correlative approaches: Group method of data handling and gene expression programming

Accurate estimation of thermal conductivity (TC) of nanofluids is essential in thermophysical studies of nanofluids. In this study, more than 3200 data of thermal conductivity of nanofluids were collected from literature to develop simple-to-use and accurate correlations for predicting relative thermal conductivity of nanofluids. The dataset includes 13 different nanofluids with temperature from −30.00 to 149.15 °C, particle size from 5.00 to 150.00 nm, particle thermal conductivity from 1.20 to 1000.00 W/mk, particle volume fractions from 0.01 to11.22%, and base fluid thermal conductivity from 0.11 to 0.69 W/mk. Group method of data handling (GMDH) and gene expression programming (GEP) as two white-box powerful models were used for modeling. The results of proposed models were compared to 23 well-known theoretical and empirical models. The statistical and graphical results showed that the proposed models are more precise and reliable than the existing ones in literature. The GMDH model showed a better performance compared to GEP, and could predict all data with an average absolute relative error of 2.27% in training and 2.44% in testing data set. In addition, it was found that the proposed models could capture the physically expected trends with variation of temperature, size of nanoparticles, and volume fraction. The sensitivity analysis illustrated that temperature has the highest effect on the relative TC followed by base fluid TC and particle volume fraction

Comprehensive Studies of the Processes of the Molecular Transfer of the Momentum, Thermal Energy and Mass in the Nutrient Media of Biotechnological Industries.

This article puts forward arguments in favor of the necessity of conducting complex measurements of molecular transport coefficients that quantitatively determine the coefficients of dynamic viscosity, thermal diffusivity and molecular diffusion. The rheological studies have been carried out on the viscometers of two types: those with a rolling ball (HÖPPLER® KF 3.2.), and those with a rotary one (Rheotest RN 4.1.). The thermophysical studies have been performed using the analyzer Hot Disk TPS 2500S. The measurements have been taken in the temperature range of 283 to 363 K. The concentration of dry substances has varied from 16.2 to 77.7% dry wt. An empirical equation for calculating the density of aqueous solutions of beet molasses has been obtained. The diagrams of the dependence of the dynamic viscosity on the shear rate in the range of 1 s−1 to 500 s−1 at different temperatures have been provided. The diagrams of the dependence of the coefficients of thermal conductivity and thermal diffusivity on the temperature and the concentration of dry substances have been presented, and empirical equations for their calculation have been obtained. The findings can be used for engineering calculations of hydrodynamic and heat-exchange processes in biotechnological equipment.

Влияние дейтерирования на фазовые переходы в (NH-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-VOF-=SUB=-5-=/SUB=-

The (ND4)3VOF5 crystal was grown with a high degree of deuteration (D ~ 92%). Structural and thermophysical studies have been carried out, the parameters of phase transitions have been determined. It was found that the deuteration of the ammonium cation in (NH4)3VOF5 led to a change in the chemical pressure, which was accompanied by an increase in the unit cell volume and an increase in the phase transition temperatures. The baric coefficients dTi / dp were determined and the phase T-p diagram (ND4)3VOF5 was constructed. A decrease in the temperature stability of the initial cubic phase Fm 3m in (ND4)3VOF5, as well as a wedging out of the intermediate monoclinic phase at a lower pressure as compared to (NH4)3VOF5, was found.

Effect of deuteration on phase transitions in (NH-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-VOF-=SUB=-5-=/SUB=-

The (ND4)3VOF5 crystal was grown with a high degree of deuteration (D~92%). Structural and thermophysical studies have been carried out, the parameters of phase transitions have been determined. It was found that the deuteration of the ammonium cation in (NH4)3VOF5 led to a change in the chemical pressure, which was accompanied by an increase in the unit cell volume and an increase in the phase transition temperatures. The baric coefficients dTi/dp were determined and the phase T-p diagram (ND4)3VOF5 was constructed. A decrease in the temperature stability of the initial cubic phase Fm3m in (ND4)3VOF5, as well as a wedging out of the intermediate monoclinic phase at a lower pressure as compared to (NH4)3VOF5, was found. Keywords: oxyfluorides, phase transitions, heat capacity, thermal expansion, pressure.

Study of optical and cooperative parameters of fibrous quartz heat shielding on experimental data on its reflection spectra

The paper presents the results of a study of a number of key optical characteristics of some highly porous thermal protection materials based on amorphous SiO2 fibers in the near and mid IR ranges. In the optical part of the statistical simulation model of such materials, based on the rigorous Mie theory, its application requires the introduction of cooperative corrections to the results of interaction with electromagnetic radiation of individual fragments. These corrections are introduced into the model in the form of an additional multiplier (Cs) of the scattering and absorption Mie efficiencies, which was usually used as a model tuning parameter when interpreting the experimental results of thermophysical studies. In this work, using the example of TZM-23M materials (Russia), made of a relatively thick (~9 μm) silica fiber PS-23 (Belarus), for the first time, data were obtained that make it possible to study the Cs parameter as a spectral quantity. The study is based on the results of experimental determination of the spectral hemispherical reflectivity of layers of material of two or more optical thicknesses in the wavelength range 0.83-16.65 μm. These data and Zege's asymptotic formulas were used to estimate the values of the absorption and scattering coefficients. The spectral parameter Cs is determined from the value of the scattering coefficient in the process of solving the inverse optical problem. The data obtained are compared with the results calculated on the basis of classical approximations of the optical constants. The results of this work can be useful for specialists in the field of radiation heat transfer and the interaction of electromagnetic radiation with complex partially transparent media with high spectral albedo scattering values. Keywords: Silica fibrous thermal protection, reflectivity, experiment, absorption and scattering spectrum, optical model, Mie theory, cooperative corrections.

Исследование оптических и кооперативных параметров волокнистой кварцевой теплозащиты по экспериментальным данным о ее спектрах отражения

The paper presents the results of a study of a number of key optical characteristics of some highly porous thermal protection materials based on amorphous SiO2 fibers in the near and mid IR ranges. In the optical part of the statistical simulation model of such materials, based on the rigorous Mie theory, its application requires the introduction of cooperative corrections to the results of interaction with electromagnetic radiation of individual fragments. These corrections are introduced into the model in the form of an additional multiplier Cs of the scattering and absorption Mie efficiencies, which was usually used as a model tuning parameter when interpreting the experimental results of thermophysical studies. In this work, using the example of TZM-23M materials (Russia), made of a relatively thick (~ 9 μm) silica fiber PS-23 (Belarus), for the first time, data were obtained that make it possible to study the Cs parameter as a spectral quantity. The study is based on the results of experimental determination of the spectral hemispherical reflectivity of layers of material of two or more optical thicknesses in the wavelength range 0.83 - 16.65 μm. These data and Zege's asymptotic formulas were used to estimate the values of the absorption and scattering coefficients. The spectral parameter Cs is determined from the value of the scattering coefficient in the process of solving the inverse optical problem. The data obtained are compared with the results calculated on the basis of classical approximations of the optical constants. The results of this work can be useful for specialists in the field of radiation heat transfer and the interaction of electromagnetic radiation with complex partially transparent media with high spectral albedo scattering values.

On the influence of ion-plasma treatment on the surface properties of reinforcing fillers

This article presents the results of a study of the hydrophilic properties of VMPS-10 84x4 glass filaments and SYT-49S 12K carbon tows. It has been found that the contact angle of glass and carbon fibers, which decreases after ion-plasma treatment, returns to its original values within 8 days. The capillarity values of both types of fibers increase irreversibly, but for carbon fibers, we observe a more significant change in this parameter. In the course of studying the microstructure of the surface of filler fibers before and after processing, it was found that all samples were uniformly covered with a film of an active lubricant with a microdispersed structure; however, for glass fibers, the size of the sizing particles increased during processing, and for carbon fibers, it decreased. In addition, thermophysical studies of the used reinforcing fillers were carried out, and it was found that during the ion-plasma modification, the erosion of the sizing film occurred.

Thermophysical studies of protonated and deprotonated glycine in aqueous sodium acetate buffer solutions at different temperatures

Interactions of glycine in water and in (0.10, 0.50 and 1.00) aqueous sodium acetate buffer solutions of pH (1.00 and 12.40) have been investigated at different temperatures, T/K = (298.15-318.15). Densities, and viscosities, of glycine in water and in aqueous sodium acetate buffer solutions have been measured. The obtained density data have been used to calculate apparent molar volume, , limiting partial molar volume, , limiting partial molar volumes of transfer, . Viscosity B-coefficient, viscosity B-coefficient of transfer, , Activation free energies per mole of the solute, and solvent, have been calculated from viscosity data. Further, second order derivative of partial molar expansion coefficient and dependence of coefficients on temperature is useful in measuring the structure making and breaking behavior of solute in these systems. Pair and triplet interaction coefficients for both the properties were also calculated. Thus, the results obtained from volumetric and viscometric studies are of considerable importance to identify different type of interactions (i.e. H-bonding, van der Waal’s interactions)in these systems.

Effect of Microstructure on Thermophysical Properties of Heat-Treated Duplex Steel.

The purpose of this study is to investigate the effect of heat treatments and resulting changes in microstructure on the thermophysical properties of commercial 1.4462 duplex stainless steel. Three types of heat treatment and a raw sample were used. In the first heat treatment, a duplex steel bar was annealed in an air atmosphere furnace for one hour at 1200 °C and then quickly cooled in water (1200 °C + water). The second heat treatment was the same as the first, but afterwards, the bar was annealed in an air atmosphere furnace for 4 h at 800 °C and then slowly cooled down in the furnace to room temperature (1200 °C + water + 800 °C). In the third heat treatment, the duplex steel bar was annealed in the furnace in an air atmosphere for one hour at 900 °C and then slowly cooled in the furnace to room temperature (900 °C). As a result, the weight percentages of ferrite and austenite in the samples achieved the following ratios: 75:25, 65:35 and 44:56. Light microscope examinations (LM), scanning electron microscopy (SEM), Vickers micro-hardness measurements and thermophysical studies using a laser flash apparatus (LFA), differential scanning calorimetry (DSC) and push-rod dilatometry (DIL) were performed to reveal the microstructure and changes in thermophysical properties including thermal diffusivity, thermal conductivity, thermal expansion and specific heat. Along with presenting these data, the paper, in brief, presents the applied investigation procedures.

Evaluation of molecular interactions in binary mixtures comprising ethylene and di-ethylene glycol with ethyl lactate through thermophysical and spectroscopic studies

In this article, the study of molecular interactions in liquid systems containing industrially and biologically important solvents with minimal environmental damage has been done. Density (ρ) and refractive index (nD) of binary systems comprising ethyl lactate (EL) + ethylene glycol (EG) and di-ethylene glycol (DEG) at various mole fractions and T = (298.15 to 313.15) K along with pure components have been measured. The observed parameters were further used for determination of excess molar volumes (VmE), partial molar volumes (V¯m), excess partial molar volumes (V¯mE), deviations in refractive index (ΔϕnD) and deviations in molar refraction (ΔϕRM). Redlich-Kister coefficients along with standard deviations have been obtained by approximation of data to polynomial equation. The obtained VmE results have been investigated theoretically by means of Prigogine-Flory-Patterson (PFP) and Graph theories to estimate type and nature of interactions among constituent molecules which can be used to explain the changes in physicochemical properties of the mixtures. By analysing experimental data in light of PFP Theory, Interactional and characteristic pressure contributions have been found negative values for both the binary systems whereas free volume contribution possess positive sign. The structural variation of the components in the mixtures due to change in molecular interactions has been discussed by Graph theory. Fourier Transform InfraRed (FT-IR) studies have also been performed for pure and equimolar mixtures to enlighten the experimental outcomes. It confirmed the rupture of pre-existing bonding in lactate and the formation of new hydrogen bonds with glycols.

Thermophysical Investigation of Asteroid Surfaces. I. Characterization of Thermal Inertia

Abstract The thermal inertia of an asteroid is an indicator of the thermophysical properties of the regolith and is determined by the size of grains on the surface. Previous thermophysical modeling studies of asteroids have identified or suggested that object size, rotation period, and heliocentric distance (a proxy for temperature) are important factors that separately influence thermal inertia. In this work we present new thermal inertia values for 239 asteroids and model all three factors in a multivariate model of thermal inertia. Using multiepoch infrared data of this large set of objects observed by WISE, we derive the size, albedo, thermal inertia, surface roughness, and sense of spin using a thermophysical modeling approach that does not require a priori knowledge of an object’s shape or spin axis direction. Our thermal inertia results are consistent with previous values from the literature for similarly sized asteroids, and we identify an excess of retrograde rotators among main-belt asteroids <8 km. We then combine our results with thermal inertias of 220 objects from the literature to construct a multivariate model and quantify the dependency on asteroid diameter, rotation period, and surface temperature. This multivariate model, which accounts for codependencies between the three independent variables, identifies asteroid diameter and surface temperature as strong controls on thermal inertia.

ОБЗОР ИССЛЕДОВАНИЙ МЕТАЛЛИЧЕСКОГО ТОПЛИВА U-10 мас. % Zr

The article provides a review of well-known foreign scientific publications devoted to the study of the properties of metallic nuclear fuel based on U-Zr, in composition close to U 10 wt. % Zr, which is widely used in reactors. Differences in the microstructure of fuel made by different methods: extrusion and casting - are considered. The effect of thermal annealing on the change in the microstructure of the alloy is shown. The photographs obtained using optical and electron microscopes are presented, as well as crystallographic data for two phases: α-U and δ-UZr2. The known literature data indicate that the density of uranium-rich U-Zr alloys corresponds to the rule of mixtures. The theoretical density of the alloy U-10 wt. % Zr (U-22.5 at. % Zr) should be taken as 16.2 g/cm3. The results of thermophysical studies of 10 wt. % Zr fuel using the method of differential scanning calorimetry (DSC) are presented. Data on measurements of thermal expansion of U-Zr alloys, as well as thermal conductivity are presented. Most of the thermal conductivity data are either calculated from the measured density, specific heat and thermal diffusivity, or obtained from simulations.

A Critical Review on the Development of Ionic Liquids-Based Nanofluids as Heat Transfer Fluids for Solar Thermal Energy

In recent years, solar thermal energy (STE) has attracted energy researchers because of its higher efficacy compared to the photovoltaic solar cell. STE is one of the forms of solar energy whereby heat is transferred via a secondary medium called heat transfer fluids (HTFs). Therefore, the overall performance of STE depends on the thermophysical properties and thermal performance of the HTFs. Traditional HTFs suffer from low decomposition temperature, high melting point, and higher vapor pressure. To overcome these limitations, researchers have recently begun working on new HTFs for STE. Ionic liquids (ILs) are considered as a potential candidate for the next generation of HTFs because of their enhanced thermophysical properties, such as thermal stability at high temperature, insignificant vapor pressure, and high ionic conductivity. In addition, thermophysical properties and thermal performance of ILs can be further enhanced by dispersing nanoparticles, which is one of the emerging research interests to improve the efficiency of the solar thermal system. This paper summarizes the recent study of ILs-based nanofluids as HTFs. These summaries are divided into two sections (i) thermophysical properties studies, such as density, viscosity, thermal conductivity, and heat capacity, and (ii) thermal performance studies such as natural convection and forced convection. Synthesis of ILs-based nanofluids and thermophysical properties measurement techniques are also discussed. Based on these state-of-the-art summaries, we offer recommendations for potential future research direction for ILs-based nanofluids.

Thermophysical studies of common wall panels for controlling building thermal environment

Urban heat island accumulatively influenced by characteristics of its building environment. A developed urban area that characterized with many building constructions shown a higher air temperature than its surrounding. Thermophysical studies of building wall were conducted involving thermal conductivity, specific heat, material density, and solar absorptivity. This paper discusses the simulation of the wall’s thermophysical characteristic with the variation of the wall’s thermal properties using Energy2D simulation program. We report the simulation of the 11 cm brick wall with an area of 1 m × 1 m, where the wall was exposed to a heat source for 4 h and then continued with 4 h cooling. The measurement results show that the absorptivity aspect of the wall determines the amount of heat distributed around the wall, while thermal conductivity and specific heat of the wall determine the heat distribution. We conclude that controlling the wall’s thermal properties will give a specific impact on the thermal environment.

ВЛИЯНИЕ ТЕМПЕРАТУРНО-ВЛАЖНОСТНОГО РЕЖИМА ЗАГЛУБЛЕННЫХ ОБЪЕМОВ НА СОХРАННОСТЬ ПАМЯТНИКОВ АРХИТЕКТУРЫ С МОНУМЕНТАЛЬНОЙ ЖИВОПИСЬЮ НА ПРИМЕРЕ СПАСО-ПРЕОБРАЖЕНСКОГО ХРАМА ГОРОДА ПОЛОЦКА

The heat and humidity regime of the buried parts can be essential, and sometimes crucial, for the normalization of the microclimate of the entire monument. The experience of thermophysical studies in church architectural monuments shows a wide range of factors that determine the impact of the temperature and humidity regime of the buried volumes on the formation of conditions for the preservation of the monument as a whole. Currently, the Climate Laboratory of Museums and Architectural Monuments of GOSNIIR conducts research on this problem in order to create a methodology for studying and normalizing the heat and humidity regime of the aboveground and underground parts of the building as a whole to develop design and technological approaches to optimizing the conditions for the preservation of the monument. The article considers a practical example of providing heat and humidity conditions for the preservation of a monument with monumental painting.

ТЕПЛОГИДРАВЛИЧЕСКИЕ ИССЛЕДОВАНИЯ ВЫСОКОТЕМПЕРАТУРНОЙ ЯЭУ ДЛЯ ПРОИЗВОДСТВА ВОДОРОДА И ДРУГИХ ТЕХНОЛОГИЧЕСКИХ ПРИЛОЖЕНИЙ

An important problem determining the development of clean energy is the involvement of hydrogen in the fuel cycle. At present, the main method of hydrogen production is steam methane conversion. In the long term, large-scale hydrogen production, this method is not viable due to the consumption of non-renewable resources and the emission of greenhouse gases. Alternative methods of hydrogen production by water splitting methods using thermochemical or electrolysis processes require a high-temperature heat source. Nuclear reactors can serve as the most widely used high-temperature heat sources. The performed neutron-physical and thermophysical studies have shown that there is a fundamental possibility to provide the required parameters of a high-temperature (900-950 °C) with a 600 MW (thermal) fast neutron reactor with a sodium coolant for hydrogen production. It’s possible on the basis of one of the thermochemical cycles or high-temperature electrolysis with a high coefficient of thermal utilization of energy. It is shown that the temperature regime of core fuel elements is determined by a large number of parameters that have a regular and statistical nature. The developed methodology and numerical program allows to take into account, in the fuel assemblies shaped during the campaign, the effect on the temperature distribution of the fuel element cladding and temperature irregularities along the fuel element perimeter in the interchannel exchange fuel assembly, the random distribution of channel cross-sections and the heat generation of fuel elements using the Monte Carlo method, also other factors. For various reactor operating regimes, zones with stable temperature stratification with large gradients and temperature fluctuations have been identified. The results obtained make it possible to judge the amplitude and frequency characteristics of temperature pulsations in these potentially dangerous areas. The relative small size, the type of coolant, the choice of fissile material and structural materials make it possible to create a reactor with inherent properties that ensure increased nuclear and radiation safety.

Correction to “Thermophysical Studies of Dibenzyltoluene and Its Partially and Fully Hydrogenated Derivatives”

Correction to “Thermophysical Studies of Dibenzyltoluene and Its Partially and Fully Hydrogenated Derivatives”

КВАНТОВО-ХИМИЧЕСКОЕ ИССЛЕДОВАНИЕ МЕЖМОЛЕКУЛЯРНЫХ ВЗАИМОДЕЙСТВИЙ В КОМПЛЕКСНЫХ СИСТЕМАХ «ПОЛИАМИД-СИЛИКАГЕЛЬ»

The paper presents the results of quantum-chemical studies of polymer composite materials based on aromatic polyamide phenylon C1 filled with silica gel. Structural models of initial compounds with indication of charges on atoms and interatomic distances are offered. The theoretical models of complexes in «polyamide-silica gel» systems have been constructed, which describe the most probable intermolecular interactions of the polymer matrix with the filler. The adequacy of the obtained models was confirmed by the results of IR spectroscopy. It has been found that the chemical interaction of polymer molecules with the filler is carried out mainly due to the formation of strong hydrogen bonds that occur between oxygen atoms of carbonyl groups in polymer molecules and active hydroxyl groups on the surface of silica gel particles. The chemical nature for intermolecular interactions of polymer with filler has also been confirmed with preliminary physico-mechanical and thermophysical studies of polymer composite materials, as a result of which it was found, that the introduction of fine silica gel particles into the structure of phenylon C1 contributes to a significant increase of the level of stress at the yield strength, modulus of elasticity in compression and hardness with a shift of the corresponding values of heat and heat resistance of the obtained polymer composites in the area of higher temperatures.

Three-dimensional modeling of female breast based on thermograms for thermophysical studies of breast pathologies

Thermographyis a technique that has been proposed as a complementary examination for the detectionof breast cancer. These images have also been used to validatethree-dimensional numerical simulations, where temperature profiles arecalculated and used for a better understanding of breast abnormalities.Therefore, the development of a realistic model would enable a better reliableestimation of the thermophysical properties of the breast and itscomorbidities. Thisstudy presents a method for the development of a personalized three-dimensionalbreast geometry from the curves manually extracted from the thermogramscontained in the thermographic image database of the Federal University ofPernambuco (UFPE). The collected images belong to voluntary patients whoreceived the complete diagnostic and were seen at Hospital das Clinicas - UFPE.With the manual extraction of the profile curve, the final 3D geometry presentsa much more similar aspect with the superficial anatomy of the female breast. Theresults obtained by numerical simulation of the temperature profile werecompared with the results obtained using previous geometry, showing that themethod proposed in this study can be successfully used for the calculationspresented. Themethod suggested by this study brought a simplification of the productionprocess of three-dimensional breast models based on thermographic images.

Assessing Lava Flow Subpixel Surface Roughness and Particle Size Distribution for Improved Thermal Inertia Interpretations

Apparent thermal inertia (ATI) is a remote sensing-based thermophysical approximation used to estimate surface properties such as particle size or soil moisture, but is subject to oversimplifications if uniform surface materials are assumed. Geological surfaces realistically contain multiple types of materials that are represented by mixed pixels in a digital image that can dramatically affect the derived thermal response. Thus, the current surface uniformity assumption can lead to erroneous calculations. To define how these mixed particle size surfaces affect ATI, a multi-instrument, multi-spectral study was conducted at the North Coulee rhyolite flow, Mono Domes (California). This flow is compositionally homogenous with particle sizes ranging from silt size to boulders, making it an ideal location to understand the relationship between particle size distributions and ATI. Multispectral data from orbital sensors with increasing spatial resolutions were analyzed in combination with samples, GPS, and photogrammetry data collected in the field. The surface particle size characteristics divided into three broad categories (fine, moderate, and coarse) were mapped based on WorldView-2 visible data and field observations. Broad categories were validated using a 3-dimensional point cloud derived from structure-from-motion (SfM) methods using field photographs. The areal percentage of each category within an ATI pixel was derived to populate a lookup table (LUT) with the corresponding ATI values to quantify the effect of mixed pixels. Lower ATI values are dominated by fine particles (sand and dust) as expected, however, surfaces with the highest values were predominately moderate-sized cobbles. Pixels with a high areal percentage of coarse sizes display an intermediate ATI value, suggesting that either self-shadowing or trapping of fines lowers the ATI value. Alternatively, areas with a majority of moderate particle sizes have less shadowing and efficient vertical sorting of smaller material, as seen in field data, leaving a thermal derived response indicative of the dominating particle size. This study demonstrates how a uniform property assumption can cause erroneous derived thermal modeling, particularly over surfaces with a high percentage of boulders and large particle sizes. Future thermophysical studies of Earth or other planetary surfaces can greatly benefit from a multi-sensor approach combined with a higher spatial resolution visible dataset.